Balloon angioplasty and stenting are widely used in the treatment of coronary artery disease and peripheral vascular disease. In coronary artery disease, one or more coronary blood vessels become narrowed or closed due to the buildup of stenotic plaques on the arterial wall. This blocks blood flow to the heart muscle, potentially causing myocardial infarction. Such narrowing can also occur in peripheral blood vessels such as the carotids, femorals, iliacs and other arteries, blocking blood supply to other vital tissues and organs.
Balloon angioplasty involves the use of a long flexible catheter having a balloon at its distal tip. The catheter is inserted into a peripheral artery such as the femoral and advanced transluminally into the diseased artery. The balloon is inflated within the narrowed portion of the vessel, thereby expanding the vascular lumen and restoring normal blood flow.
In some cases, however, balloon angioplasty alone is inadequate to treat vascular disease due to restenosis, the renarrowing of the artery following angioplasty. Stents have been developed to provide an intravascular frame or scaffold to maintain patency of the vascular lumen after it has been expanded. Stents are small tubular prostheses designed to be advanced to the treatment site in a collapsed configuration using an elongated delivery catheter. The stents are then expanded at the treatment site into engagement with the vessel wall to maintain vascular patency.
Stents may be either self-expanding or balloon expandable. Self-expanding stents are made of a shape memory material such as Nitinol and can be delivered in a compressed state within the tip of the delivery catheter and allowed to resiliently expand upon release from the delivery catheter. Balloon expandable stents are made of a malleable metal and are mounted to a balloon on the delivery catheter. When positioned at the treatment site, the balloon in inflated to expand the stent into engagement with the vessel.
Stents, however, have also suffered from the problem of restenosis. Restenosis rates with conventional coronary stents have ranged from 30-40%. The causes of such restenosis are not fully understood. However, it is believed that restenosis may be caused in some cases by the excessive stiffniess of current stents and their inability to conform to vascular curves, shapes, dimensional changes, and movements. This problem is particularly acute with longer lesions, which may extend over curved and tapered sections of a vessel and may be subject to non-uniform movements along their lengths.
The need has thus been demonstrated for highly-flexible stents that may be used to treat long, curved, and tapered vascular regions. In co-pending U.S. patent application Ser. No. 10/637,713, filed Aug. 8, 2003, entitled “Apparatus and Methods for Delivery of Vascular Prostheses, the full disclosure of which is incorporated herein by reference, highly flexible multi-segmented stents and associated delivery devices are disclosed that enable the treatment of long, curved or tapered vascular lesions. The disclosed delivery devices enable the selective deployment of one or more stent segments at a treatment site to allow the user to customize stent length in situ. Moreover, the device can be repositioned at multiple vascular sites to deploy a plurality of stents at various lengths.
Other custom-length stents and delivery devices are described in co-pending U.S. patent application Ser. No. 10/624,451, filed Jul. 21, 2003, entitled “Apparatus and Methods for Delivery of Multiple Distributed Stents,” which is also incorporated herein by reference. This application describes separable stent segments as well as continuous prosthesis structures configured as braids or coils that allow the user to pay out a selected length of the prosthesis structure and deploy it into the vessel at one or more treatment sites.
Variable length angioplasty devices have also been proposed. For example, U.S. Pat. No. 5,246,421 to Saab discloses angioplasty catheters having an elongated balloon and an external sheath that is axially slidable relative to the balloon. The sheath can be retracted to expose a selected length of the balloon for expansion at a treatment site. The catheter can then be repositioned and another length of balloon exposed to treat one or more additional sites.
The need has thus also been demonstrated for improved ways of controlling and providing indication of balloon and stent length in angioplasty and stenting catheters and other devices. In co-pending U.S. patent application Ser. No. 10/746,466, filed Dec. 23, 2003, entitled “Devices and Methods for Controlling and Indicating the Length of an Interventional Element,” the full disclosure of which is incorporated herein by reference, devices and methods are disclosed that control an interventional element through the use of gear driven actuators, motors, and other mechanisms. The disclosed devices provide an indication to the user of the length of an interventional element by the use of sensors, detents, visual displays and other mechanisms that provide visual, audible, and tangible indications of length to the user. The disclosed control and indication devices preferably operate in tandem to enable highly precise adjustment of interventional element length.
While such custom-length stents, angioplasty catheters, and controlling and indicating devices have shown great promise, there remains a need for improved ways of controlling and operating interventional apparatus such as angioplasty and stenting catheters.